Our memories are important. They make us who we are. They allow us to be a part of our world, and our friends and families’ too. Most importantly, they allow us to have a common experience, and share a common bond.
But what is memory?
When I was in graduate school, psychologists had developed the constructs of long-term and short-term memory. Short-term memory was famously codified by George Miller in his seminal paper The Magical Number Seven Plus or Minus Two. (It was a good paper, an even better title.) I say codified because in fact humans had figured this out. Phone numbers were 7 digits, zip codes were 5, etc. After reviewing the research, Miller concluded that humans can easily remember between 5-9 digits…but these numbers did not always get into long-term memory.
At the time, we assumed that long-term memory was like a filing cabinet, where we stored each memory. An inability to remember was due to the filing cabinet being full or being unable to find the “file.”
Without measures of brain functioning, all we could do were studies on memory, creating hypotheses based on recall or recognition and how memories were acquired, e.g., classical conditioning (where we pair two stimuli) and operant conditioning (where we reward behavior).
As usual in science, the advent of measurement allowed us to learn more about memory and made scientists aware that these views were way too simplistic.
Brain imaging studies revealed that a single memory is actually stored in multiple places. We have separate places in the brain where we store the sensory part of memory (taste, smell, sound, touch, visual), others where we store observations or events, and still others that store automatic memories (e.g., how to tie a shoe; how to drive a car).
The act of remembering requires the brain to locate and coordinate all of the information associated with that single memory from multiple parts of the brain. Instead of a single file we have multiple files of the same event and a mechanism for knowing which memories are connected to each other.
Even the amygdala gets involved. As many know, the primary function of the amygdala is to regulate emotions, such as fear and aggression. The amygdala plays a part in how memories are stored because storage is influenced by stress hormones. Also, we store that feeling from that event (e.g., phobias). In a study, researchers encoded fear memories in mice using classical conditioning, in this case pairing a shock with a tone. The amygdala allowed the mice to remember that a tone is associated with a shock, and they learned to fear the tone. It is suspected that this amygdala encoding is a source of anxiety, PTSD, phobias, and other psychological conditions. Some researchers have been successful in eliminating phobias using repeated exposure, and, more recently with lasers and injected drugs to directly impact the neurotransmitters and eliminating the association of the fear response.
The concepts of short and long-term memory are based on how long we store the memory. Before reaching long or short-term memory, information perceived by our senses and may be encoded into sensory memory (e.g., recognizing a red fire truck), which is immediate and fleeting. If we pay attention to that sensory memory (e.g., the fire truck) we can bring it to short-term memory (which lasts for 15-30 seconds). Then, in some cases, short-term memory transfers that memory to long-term memory.
Working memory is a type of memory that is often confused with short-term memory. Working memory uses both short-term information and requisite memories from long-term memory. (For example, when adding two numbers; the brain combines the short-term memory for the 2 numbers, plus the long-term memory of how to add.)
There are many types of long-term memory. For example, the memory to do an automatic task, such as tying a shoelace, involves different parts of the brain than recalling what we had for dinner last night.
The memory for tying a shoelace is called procedural memory or implicit memory. These are tasks we don’t need to consciously think about before we do them, for example, typing (if you learned how to type), writing, pouring water into a glass. Multiple parts of the brain are used to process and coordinate the muscle movements and steps. The basal ganglia (in the middle of the brain) and the cerebellum (near the brain stem) are most involved in coordinating the memories required to perform an automatic task. (But don’t forget the amygdala, if this task generates a fear response, such as pouring boiling water.)
Declarative or explicit memories, on the other hand, are consciously remembered events (such as someone’s name); basically, what most of us think of when we think of memory. It uses the hippocampus, which is a seahorse-shaped structure in the middle of the brain and the prefrontal cortex, located in the front of the brain.
And yes, there are other types of memories (we are rounding the curve, folks, I promise). Spatial memories capture geographically where an object is.
Semantic memory stores explicit facts and pieces of knowledge (e.g., what a horse looks like, your son’s birthday), while episodic memory stores events and occurrences (e.g., riding a horse, his 2nd birthday party).
Then there are the sensory memories: echoic memory, iconic memory, and haptic memory. Iconic memory retains sight information, echoic memory retains auditory information and haptic memory retains sensation or touch information.
Autobiographical memories are the memories that make us human and connect to others. They are typically combinations of semantic and episodic memories that contribute to our sense of self—your own life history and identity (Am I smart? Am I nice?).
See how complex it is? And, I believe that we are just getting started. The better the tools, the more we will learn.
My big question is “Okay, we know where memory is stored, but how does it get stored? How does the brain remember?”
Scientists believe that memories are created at synapses, by building new neurological connections. Simplistically, neurotransmitters connect the synapses, and the hippocampus helps the brain build new connections.
But here is the rub. And it is very, very important.
Scientists have discovered that the same neurotransmitters used to build memory connections are also used to recall a memory. And these neurotransmitters continue to build connections during recall, which enables the building of new connections capable of changing the original memory. That means that simply the act of recalling a memory can cause us to alter the original memory by using the same neural transmitters to add new connections to that memory.
Think about that, and its implications. Just the act of recalling a memory can cause us to change any of those types of memories!
The process allows us to add features of the present day to the original memory. I have done this many times. For example, when I am trying to recall where I left something, let’s say, my phone. I frequently create a memory that I placed it in a location that I did not. I can “recall” the color of the table, the room, the time of day, and the sound of it ringing. I created this false memory as part of the act of trying to recall where I left my phone.
Scientists have been able to successfully implant false memories in most subjects just through suggestion. Some “memories” are outlandish and can even go against that person’s nature.
For example, one gentle subject “remembered” that she had been in a fight with a friend and the police were called. That never happened. The researchers did this by telling the subject about this fight while the subject was recalling a related memory. In this example, the subject was asked the year, the park, and the name of the friend. The researcher then asked her, “Don’t you remember the fight you had with your friend in that park? Your parents described a fight with this friend where the police were called.” At first, the subject denied it. But over several sessions, the researcher continued to ask the subject about that fight while asking her to recall the related information. Over time, the subject added that false memory to hre original memory.
Think about the implications for us. It is one of the reasons that eyewitness testimony is often inaccurate. We build new connections for sensory, semantic, autobiographical, explicit, geographical, and other memories into the actual memory when we recall the event. How many times have you spoken to a person where you shared a “memory” and you had different dates, locations, etc.? You had the event memory of being together, but everything else was changed.
Today, we have video on cell phones to the capture the actual event. It can only help all of us because our memories have too many opportunities to fail.
Scary, isn’t it?
Angela Rieck, a Caroline County native, received her PhD in Mathematical Psychology from the University of Maryland and worked as a scientist at Bell Labs, and other high-tech companies in New Jersey before retiring as a corporate executive. Angela and her dogs divide their time between St Michaels and Key West Florida. Her daughter lives and works in New York City.